1. Field of the Invention
The present invention generally relates to fuel injection control systems for outboard motors. More particularly, the present invention relates to such control systems that reduce power output disparities between cylinders and that reduce fuel injector temperatures during certain periods of engine operation.
2. Related Art
By their nature, multi-cylinder marine engines used in outboard motors are compact. This means that the air induction and exhaust systems for these marine engines are not symmetric with respect to the various cylinders in the engine. For this reason as well as others, the operating conditions for the specific cylinders in the two-cycle engine vary greatly. For instance, differences in air motion within the cylinders can substantially affect the amount and quality of air/fuel mixing prior to combustion. Also, due to the different lengths of air intake paths and exhaust tuning paths, the effectiveness of the scavenging process among the cylinders varies, thus changing the quality of preparation in the cylinder before combustion. Further, exhaust and/or induction tuning effects can substantially alter the air/fuel ratio among the various cylinders (e.g. more air is provided to cylinders with relatively greater pressure pulse supercharging). All of these factors substantially alter combustion characteristics from cylinder to cylinder. It is difficult to account for these differences, especially over a wide range of operating conditions.
In addition, cylinder wall temperatures also tend to vary because it is difficult to provide an engine cooling system that maintains all of the cylinder wall temperatures at the same or substantially the same temperature. This is especially difficult because the combustion characteristics of the various cylinders provide different amounts of heat and these variations change with engine speed and load.
In direct fuel injection engines (i.e. fuel injection through the cylinder head), it is known to adjust fuel injection time and quantity on a cylinder-specific basis to account for some of the differences among combustion characteristics for the various cylinders. Some of these adjustments have been based upon the temperature of the cylinder wall, which has a large thermal mass and, therefore, does not change temperature very quickly.
In direct fuel injected engines, a spray of fuel is injected directly into the combustion chamber and is directed at least in part over the spark plug electrodes. At idle and light loads, the air/fuel mixture in the combustion chamber is dramatically stratified. In other words, the air/fuel mixture resulting from the fuel spray is fuel rich around the spark plug electrodes, whereas the mixture in the remaining portions of the combustion chamber contains less fuel. At idle and light loads, stratified air/fuel charges result in better combustion efficiencies. At higher engine speeds and loads (i.e., medium to high), stratified charges are not very suitable due to combustion characteristics.
Another difficulty with outboard motor direct-injected engines results from the asymmetric induction and exhaust systems. The asymmetry results in differing scavenging efficiencies, charging efficiencies, power outputs, cylinder temperatures and other difficulties. In marine applications, these difficulties often are amplified due to the increased periods of operation at high speeds and high loads. The prolonged high speed and high load operation often cause aggregation of residual exhaust gases that further exasperate the differences from cylinder to cylinder.
Accordingly, a control system is desired that can quickly reduce relative variations in power output from cylinder to cylinder in a multicylinder engine. The control system preferably reduces the temperature of fuel injectors operating above a normal temperature range. The control system also preferably increases the power output, and therefore the temperature, of fuel injectors operating below a normal range. The control system can be programs with correction factors based on engine speed, engine load and fuel injector nozzle temperatures.
One aspect of the present invention comprises an engine for an outboard motor comprising a plurality of cylinders having a corresponding plurality of combustion chambers. The engine also comprises an engine speed sensor, an engine load sensor and a corresponding plurality of fuel injectors disposed to inject fuel directly into the combustion chamber. Each of the fuel injectors has a nozzle and a temperature sensor adapted to output a signal indicative of a temperature of the nozzle. A controller receives the signal from each of the temperature sensors. The controller also receives a speed signal from the engine speed sensor and a load signal from the engine load sensor. The controller is adapted to change a control variable for each cylinder depending upon the signal from the temperature sensor associated with the cylinder, the control variable also being dependent upon the speed signal and the load signal.
Another aspect of the present invention comprises a method of controlling a direct injection multi-cylinder engine in an outboard motor. The method comprises sensing an engine speed and an engine load, determining a base control amount that is dependent upon engine speed and engine load for each cylinder, sensing the nozzle temperature for each cylinder, determining a compensation factor for each cylinder, calculating a control value for each cylinder having a nozzle temperature above a preset temperature, calculating a control value for each cylinder having a nozzle temperature below a preset temperature and output the control values to the each cylinder.